Optical communication systems have continued to gain popularity in today's data transmission markets. Primarily because of their fast transmission speed and relatively precise manufacture, optical communication systems incorporating numerous optical devices and assemblies have become the systems of choice for technology companies desiring high-speed information transmission capabilities. Accordingly, as the transfer of information becomes one of the most valuable commodities in the world, optical device manufacturers are eager to develop further improvements in optoelectronic technology.
One area relating to optical devices that has seen significant improvement in recent times is in optical interferometers often associated with optical transmitters. More specifically, interferometers, which are instruments that can measure a length in terms of the length of a wave of light by using interference phenomena based on the wave characteristics of light, have been employed in optoelectronic laser devices found in optical transmitters. In such applications, interferometers are used as wavelength lockers to select and stabilize the desired wavelength of the laser generated in the transmitter by determining a precise relationship between the intensity of optical interference and wavelength of the laser. Perhaps the most common types of interferometers employed as wavelength lockers use Fabry-Perot etalons to create the needed lightwave interference. A Fabry-Perot etalon is typically constructed from two flat translucent plates separated by a parallel spacer, all three of which have an index of refraction associate therewith, with the inner surfaces of the plates coated with a partially reflecting layer. When the etalon is placed in a beam of light, it produces a multiple beam interference that may be measured to assist in locking the wavelength of a laser within an optical transmitter.
Unfortunately, such conventional interferometers suffer from several disadvantages, primarily because of the response of the conventional etalons employed therein. For example, the response of conventionally used etalons may present issues with low slope regions, poor modulation depth, back-reflection, small Free-Spectral-Range (FSR), and high manufacturing cost.
In conventional interferometers, the reflectivity of the two etalon surfaces is typically selected to strike a balance between low-slope regions and modulation depth of the interference signal generated from the etalon. Due to the multiple-beam interference produced in a conventional etalon, the reflectivity of the etalon has opposing effects on the low-slope regions versus the modulation depth of the output signal. More precisely, if the modulation depth is increased by increasing the reflectivity, the low-slope regions also increase, which is undesirable and tends to limit their capabilities as wavelength lockers.
In addition, the reflective coating between the first plate and the parallel spacer often causes at least a part of the incoming optical signal to be reflected back to the laser. Thus, conventional etalons usually require mounting at an odd angle in the interferometer, or the placing of an isolator between the incoming optical signal and the etalon, to prevent back-reflection of the incoming optical signal back to the laser. However, if an etalon is placed at such an angle, the output of the etalon usually becomes very sensitive to even minor mechanical changes or deformations of the interferometer. Consequently, the manufacturing tolerances become very tight, which results in a relatively prohibitive design to manufacture. Although an isolator may be used, as mentioned above, its use adds to manufacturing costs and process time, as well as inventory costs.
Furthermore, the thickness of the parallel spacer of the etalon is often increased in an attempt to shorten the FSR (e.g, shorten the distance (in frequency space) between adjacent transmission peaks) of the output interference signal. However, current trends in the design of optical laser packages, which are typically fixed by the telecommunications community, typically do not offer ample space. As a result, optical components in such packages typically need to be compact. Thus, increasing the size of the etalon in any respect is highly undesirable.
Accordingly, what is needed in the art is an interferometer for use as a wavelength locker in optical laser devices that does not suffer from the deficiencies found in the prior art.